1. Field of the Invention
The present invention relates to a device for monitoring surroundings of a vehicle, a particularly to, the device mounted on a door mounted exterior mirror for detecting existence of a passing-over vehicle, a translation vehicle, or the like over a range between a rear and sides of lanes adjacent to a lane where a driver's own vehicle runs, in order to judge, for example, whether or not it is safe to change or join a main track, and also to constantly monitor safety in this range and presence of obstacles, such as vehicles.
2. Discussion of Background
In a conventional technique, it is proposed that a radar device is widely used for a device for monitoring surroundings of a vehicle, a device for controlling following-on distance and so on, equipped in vehicles. The radar device equipped in the device for monitoring surroundings of a vehicle has a structure including a fender mounted exterior mirror and a fender, as disclosed in, for example, JP-A-54-45040.
However, in recent years, it is very rare that fender mounted exterior mirrors are equipped in generally manufactured passenger cars, and door mounted exterior mirrors are equipped in almost all of passenger cars.
Further, in the above JP-A-54-45040 utilizing the fender mounted exterior mirror, a radar is formed by an independent unit separated from the fender mounted exterior mirror, wherein a specific structure that the fender houses receiving the radar is required in a vehicle body, and therefore the structure becomes complicated.
In case that a single antenna is commonly used instead of a transmitting antenna and a receiving antenna, it is necessary to provide an isolator in an electric circuit for preventing propagation of transmitted electromagnetic waves from directly turning toward a circuit of receiving system. In this, the isolator is a switch called a circulator, which is operated at a relatively high speed for separating reception from transmission in a time sequence.
Further, a visible range by a door mounted exterior mirror is generally about 25 degrees in horizontal directions, and it is well known that a range other than the visible range becomes a blind spot. Especially, in adjacent lanes within a point-blank range, an object vehicle positioned relatively close to lanes next to the adjacent lanes, namely, a position relatively apart from a driver's own vehicle, is physically and completely enclosed in a blind spot and such an object vehicle is not reflected in the door mounted exterior mirrors. Under such a situation, it is very dangerous that the driver's own vehicle changes lanes. Therefore, a driver is ordinarily instructed to directly observe the blind spot for confirming safety by swinging his head just before changing lanes.
Further, miniaturization is required for these kinds of on-vehicle equipments, in a first priority. Therefore, it is necessary to optimize an arrangement of an antenna and a radome in a device for miniaturization.